A filter system for fuel of an internal combustion engine of a motor vehicle is disclosed in EP 1 702 662 A1. The filter system has an electrical heating unit for heating the fuel. Further, the filter system has a filter housing with an inner chamber in which a filter element is arranged. The filter element separates an inlet for the fuel from an outlet. The heating unit for the liquid is removable and fitted to the filter housing in a leak proof manner. A board of the heating unit projects into an upstream region of the housing inner chamber which is bounded by the filter element. The board carries a plurality of heating elements of the heating unit. The board can be realized as an electronic card which comprises a substrate on which one or more heating tracks are printed. The substrate likewise comprises a self-regulation device, which, for example, is realized by means of a power transistor and a control circuit, the measuring system of which is a resistor with a negative temperature coefficient. In its lower section, the electronic card has two copper pads which are arranged in a water collection chamber. A water level sensor for the water level at the bottom of the housing is realized by the copper pads.
The invention is based on the object of designing a fuel filter and a heating sensor module of the kind mentioned in the introduction which is as compact as possible and by means of which the temperature of the fuel can be regulated as simply, efficiently and in as controlled a manner as possible.